The present invention relates to a pivoting load-bearing assembly including a force sensor arranged to measure a force in a particular direction, for example, to measure a clamping force in a load clamp for a lift truck, such as a carton clamp for use in handling large household appliances packed in corrugated cardboard cartons, or a paper roll clamp for handling large paper rolls in warehouses.
Lift trucks used for handling goods in warehouses may be equipped with specialized load clamping attachments intended to grip various types of loads securely. A lift truck may have a specialized paper roll clamp or a carton clamp including a pair of upright generally planar clamp arm assemblies extending forward from the lift truck and supporting generally parallel, opposed clamp pads. The clamp arms of load clamps are movable toward or away from each other laterally of the lift truck in order to grip or release a load.
As for carton clamps, while most cartons or similar containers have parallel upright sides, because of the nature of the goods inside the carton and other packing material within the outer skin of a carton, while it is generally desired to provide an even clamp force distribution, that may be difficult to achieve because of various mechanical factors. In some situations, it may be desirable to provide pressure against the exterior of a carton of a certain type in an uneven distribution, such as by providing greater pressure near the bottom of a carton and lesser pressure near the top of the part of the carton engaged by the clamp arm assembly. Similarly, it may be desirable to provide a certain distribution of clamping pressure on the other types of loads such as paper rolls. For some loads, such as large tires, it may be important to know the total force exerted by a load clamp. In these and other situations, it would be useful to know how much pressure is actually applied to a load as it is being grasped. While it has been known to calibrate lift trucks and control force by controlling hydraulic pressure, it is desired to have an actual clamping force measurement available during operation.
It is desirable for the clamp pad or clamp pads of a carton clamp to be free to at least a small extent, in order to accommodate clamp arm deflection and conform better to the shape of a carton and, to some extent, the contents of the carton. This capability is addressed in prior art Ehmann, U.S. Pat. Nos. 2,681,162 and 2,684,387, Link, U.S. Pat. No. 3,643,827, Farmer, U.S. Pat. No. 4,145,866, and Farmer, et al., U.S. Pat. Nos. 2,844,403 and 3,145,866, for example, which disclose clamp pads mounted on carton clamp arms in ways which allow a small amount of articulation.
Dosso et al. (U.S. Pat. No. 8,517,440) discloses a lift truck clamping attachment for handling cartons in which clamping pads are mounted so as to be adjusted so that the pressure provided by the clamp pads provides a desired distribution of the clamping pressure on the packages to be hoisted and transported.
It is known that strain gauges can be incorporated in large shackle pins or pivot pins or axles supporting, for example, sheaves for load-carrying cables of cranes, to provide electrical signals representative of a load to which such a shackle pin or axle is subjected, but use of such a strain gauge arrangement in a smaller pivot pin or axle may not be practical, and is quite costly, may require greater manufacturing precision than is desirable in the fit of such a pin to a set of bores in which the pin is to located, and may compromise the strength of the pivot pin in situations where relatively small forces are to be used yet are desired to be measured accurately. Additionally, such load pins are not well adapted to use in situations where bending forces in other than the direction of interest may be applied to such pins.
It is therefore desired to have a pivoting load-carrying assembly including an arrangement in which a force exerted in a particular direction by the load-carrying assembly can be measured in an isolated manner.